South Africa-born Pietersen was sacked by England in February 2014 after running into repeated confrontations with teammates and the management.
The 34-year-old rejected a fat Indian Premier League (IPL) contract for county cricket in a bid to play international cricket for his adopted country.
Pietersen scored a career-best 326 not out for Surrey against Leicestershire in the County Championship on Monday to boost his England aspirations, but was told of the ECB decision hours after his stupendous effort.
Strauss said there was a "massive trust issue" between himself and Pietersen.
"Nobody has doubted his ability as a player, his record stands up in cricket. But over months and years the trust between him and the England and Wales Cricket Board has eroded," Strauss was quoted as saying by Sky Sports on Tuesday.
"There is a massive trust issue between me and Kevin, I wish it wasn't the case. Because of that we decided it was in the best short-term interests for him not to be part of the team. I can't give him any guarantees but nobody knows what will happen in the future," he added.